In glassware forming apparatus a gob of molten glass is fed to a blank mould in which there is formed a parison which is a first stage in the formation of an article of glassware such as a bottle or a jar. Because the blank mould is continually receiving gobs of molten glass the blank mould becomes heated to a high temperature and heat must be dissipated from the blank mould in order to provide for the extraction of a necessary quantity of heat from the gob during the formation of the parison.
Conventionally, cooling of the blank mould is effected using a cooling gas, usually air. However, there exists, around the outer mould surface, a boundary layer of air which becomes heated to a temperature close to that of the outer mould surface and which is resistant to movement because of its closeness to the outer mould surface. Consequently this boundary layer of air constitutes an insulating layer which inhibits good heat transfer from the outer mould surface to the cooling gas. The boundary layer of air is penetrated by cooling gas where the cooling gas is directed at the outer mould surface, for example by jets. Provision has to be made for the cooling gas to exhaust between the jets and it has proved that adequate cooling of the blank mould by conventional means has required the use of either very high air pressures or very large volumes of the cooling air, both of which have their disadvantages.